I'm just learning illustrator CS4, though I have been using another vector drawing program for years.

When I zoom into a gradient filled rectangle created in CS4, I can see the boundaries between the color transitions. In the other vector program, I can fix this by increasing the bit depth from 8 to 16 bit (or something similar). How do I do this in illustrator?

It is most definitely NOT smooth even to my naked eyes. To be sure, copy the image into photoshop and perform an unsharp mask. Set the amount to max and keep increaseing the radius. Eventually you will see many vertical stripes, like this:

Check the document color mode and color profile settings, both on the doc and for proofing on the monitor. If the gradient is quantized, then clearly AI thinks it is necessary to avoid out of gamut issues of some sort. Otehr than that - yeah, probably a screen issue. Also keep in mind, that AI does not recalculate stuff just when zooming. This may actually be what happens in program X, so it would actually be giving you an incorrect representation of the final result...

function(){return A.apply(null,[this].concat($A(arguments)))}To be sure, copy the image into photoshop and perform an unsharp mask. Set the amount to max and keep increaseing the radius. Eventually you will see many vertical stripes...

??

Well, of course you would. That's what Unsharp Mask does: increases ("sharpens") the difference in color values between adjacent pixels which its algorithm considers "different." So given a linear gradient, when would you not expect Unsharp Mask to result in visible bands at high settings?

What is "the other vector program"? (No one is going to ban you from stating the name of a non-Adobe software.) What platform are you on?